Metallurgical furnaces of various types are used to produce metals. The process usually involves high temperatures, with the product being molten metal and process by-products, generally slag and gases. Furnace walls may be lined with cooling elements, which are typically comprised of copper or cast iron and may include internal flow passages for circulation of a coolant, typically water. For example, the walls of blast furnaces are typically lined with water-cooled cooling elements such as stave coolers and/or tuyere coolers.
Stave coolers are subject to wear caused by contact with hot, abrasive materials present inside the furnace. For example, in a blast furnace, the stave coolers are in contact with a downwardly descending feed burden comprising coke, limestone flux, and iron ore. The descending burden is hot, contains particles of various sizes, weights and shapes, and its hardness is higher than the hardness of materials typically used to manufacture a stave. Consequently, the stave coolers tend to wear out, and worn out stave coolers are typically shut down, meaning that no cooling takes place, and the stave deteriorates completely. This causes the furnace shell to overheat, which, in turn, can lead to a rupture of the shell.
Tuyere coolers are subject to erosion of the inner walls due to gas-entrained carbon-based solids; and abrasion and erosion of the outer wall due to contact with unburned carbon-based solids and molten metal drips. Consequently, tuyere coolers are highly susceptible to wear, leading to water leakage. Worn tuyere coolers are shut down and must be replaced, since damaged tuyeres lower productivity of the furnace and distort circumferential symmetry of hot air injection. This results in production losses and increased throughput through other tuyeres, which increases their likelihood of failure and may result in financial loss due to lost production.
Attempts have been made to improve the wear properties of stave coolers. For example, it has been proposed to attach wear-resistant elements to the working face of a copper stave by means of rotational friction welding, or to deposit a wear-resistant coating on the working face.
It has also been proposed to disperse hardened particles throughout the entire volume of the cooler (e.g. in JP 2001-102715 A). However, due to the relatively high cost of the hardened particles, this approach can be uneconomical since it places most of the wear-resistant particles in areas of the cooler which are not subjected to wear. Also, because the particles are small and dispersed throughout the cooling element, it is difficult to non-destructively evaluate whether they are present at the working face in sufficient concentrations.
It has also been proposed to insert abrasion resistant materials into the bottom of a mold prior to casting of a stave cooler (WO 79/00431 A1). Proposed materials include hard aggregate, such as cemented tungsten carbide, or a stainless steel expanded-metal mesh.
However, mere placement of the abrasion resistant material into the bottom of the mold does not ensure that it will be reliably located at the working face of the cooler in sufficient concentrations, making it difficult to produce a cooling element with consistent abrasion-resistance across its entire working face. While this may be acceptable for plate coolers, which can be readily replaced from the exterior of a blast furnace, it is not acceptable for stave coolers which cannot be replaced without extended downtime.
There remains a need for furnace cooling elements with improved wear properties to improve efficiency of furnace operation and minimize down-time, while maintaining low cost and manufacturability of the cooling elements.